Positive airway pressure system and method for treatment of sleeping disorder in patient

ABSTRACT

Described are a positive airway pressure system and method for treatment of a sleeping disorder in a patient. The system includes a generator, a sensor and a processing arrangement. The generator supplies airflow and applies a pressure at to an airway of a patient. The sensor measures data corresponding to patient&#39;s breathing patterns. The processing arrangement analyzes the breathing patterns to determine whether the breathing patterns are indicative of at least one of the following patient&#39;s states: (i) a regular breathing state, (ii) a sleep disorder breathing state, (iii) a REM sleep state and (iv) a troubled wakefulness state. The processing arrangement adjusts the applied pressure as a function of the patient&#39;s state.

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is a well recognized disorderwhich may affect as much as 1-5% of the adult population. OSAS is one ofthe most common causes of excessive daytime somnolence. OSAS is mostfrequent in obese males, and it is the single most frequent reason forreferral to sleep disorder clinics.

OSAS is associated with many conditions in which there is an anatomic orfunctional narrowing of the patient's upper airway, and is characterizedby an intermittent obstruction of the upper airway occurring duringsleep. The obstruction results in a spectrum of respiratory disturbancesranging from the total absence of airflow (apnea) to significantobstruction with or without reduced airflow (hypopnea and snoring),despite continued respiratory efforts. The morbidity of the syndromearises from hypoxemia, hypercapnia, bradycardia and sleep disruptionassociated with the apneas and subsequent arousals from sleep.

The pathophysiology of OSAS has not yet been fully worked out. However,it is well recognized that obstruction of the upper airway during sleepis in part due to the collapsible behavior of the supraglottic segmentof the airway resulting from negative intraluminal pressure generated byinspiratory effort. Thus, in patients suffering from OSAS, the upperairway during sleep behaves substantially as a Starling resistor (i.e.,the airflow is limited to a fixed value irrespective of the driving(inspiratory) pressure). Partial or complete airway collapse may thenoccur with the loss of airway tone which is characteristic of the onsetof sleep and which may be exaggerated in OSAS.

Since 1981, positive airway pressure (PAP) therapy applied by a tightfitting nasal mask worn during sleep has evolved as the most effectivetreatment for OSAS, and is now the standard of care. The availability ofthis non-invasive form of therapy has resulted in extensive publicityfor OSAS and the appearance of large numbers of patients who previouslymay have avoided the medical establishment because of the fear oftracheostomy. Increasing the comfort of the PAP system has been a majorgoal of research aimed at improving patient compliance with the PAPtherapy.

PAP therapy has become the mainstay of treatment in Obstructive SleepDisordered Breathing (OSDB), which includes Obstructive Sleep Apnea,Upper Airway Resistance Syndrome, Snoring, exaggerations of sleepinduced increases in the collapsibility of the upper airway and allconditions in which inappropriate collapsing of a segment of the upperairway causes significant un-physiologic obstruction to airflow. Thiscollapse generally occurs whenever pressure in the collapsible portionof the airway decreases below a level defined as a “critical tissuepressure” in the surrounding wall. The PAP therapy is directed tomaintaining pressure in the collapsible portion of the airway at orabove the critical tissue pressure at all times. In the past, this goalhas been achieved by raising a pressure delivered to the patient'sairway to a level higher than this critical tissue pressure at all timeswhen the patient is wearing the device. In general, the need for the PAPtherapy occurs only during sleep. However, the conventional PAP therapyhas not taken sleep/wake state into account, and conventional PAPsystems apply pressure unnecessarily when the patient is awake. Theapplied pressure is either a constant pressure, or a pressure based onbreath-by-breath determination of the need for treatment. Variousstrategies for determining the minimal pressure have evolved based onrecognizing pathological events (e.g., apnea, hypopnea and otherevidence of high airway resistance)as determined by feedback from avariety of signals that indicate the need for the PAP therapy due to theairway collapse.

Despite its success, limitations on the use of the conventional PAPsystems still exist based on, for example, discomfort from the mask andthe pressure required to obliterate the apneas. In particular, patientsoften report discomfort due to high pressure while being awake. To avoidthis discomfort, the applied pressure should be provided only when thepatient is asleep. For example, a “ramp” system utilizes a patientactivated delay in the onset of the applied pressure, but the rampsystem is not automatically responsive to patient awakenings during thenight, unless deliberately activated by the patient pushing a button.

Patient's discomfort during wakefulness is often associated with changesfrom a regular breathing pattern (e.g., near constant breath size andfrequency) to one which contains irregularities. These irregularpatterns (e.g., including isolated big breaths, short pauses, andchanges in breath flow shape that do not vary in any regular pattern)arerecognized by inspection of the airflow tracing alone, and frequentlyoccur when the patient is distressed by the PAP system.

Some conventional PAP systems utilize algorithms which continuously andautomatically titrate the applied pressure. These algorithms depend ondetecting evidence of airway collapse from the breathing signals.However, these algorithms of the conventional PAP systems have certainlimitations. For example, the irregular pattern of breathing presentwhile a subject is awake, and more so when anxious, interferes with theprocessing of the breath signal that calculates the applied pressure

SUMMARY OF THE INVENTION

Described are a positive airway pressure system and method for treatmentof a sleeping disorder in a patient. The system includes a generator, asensor and a processing arrangement. The generator supplies airflow andapplies a pressure to an airway of a patient. The sensor measures datacorresponding to a patient's breathing pattern. The processingarrangement analyzes the breathing patterns to determine whether thebreathing patterns are indicative of at least one of the followingpatient states: (I) a regular breathing state, (ii) a sleep disorderbreathing state, (iii) a REM sleep state and (iv) a troubled wakefulnessstate. The processing arrangement adjusts the applied pressure as afunction of the patient's state. Those skilled in the art willunderstand that the regular breathing state will include both an apneafree sleeping and a relaxed wakeful state of the patient, while thetroubled wakefulness state is one in which anxiety to discomfort of thepatient results in irregular breathing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which are incorporated in and constitute partof the specification, illustrate an embodiment of the invention and,together with the description, serve to explain examples of the presentinvention. In the drawings:

FIG. 1 shows an exemplary embodiment of a system according to thepresent invention;

FIG. 2 shows an exemplary embodiment of a method according to thepresent invention which utilizes the system shown in FIG. 1;

FIG. 3 shows a waveform of airflow during regular wakefulness of apatient (e.g., not anxious) who utilizes the system according to thepresent invention;

FIG. 4 shows a waveform of airflow during regular sleep in a patient;

FIG. 5 shows a waveform of airflow from a sleeping patient which isindicative of an elevated upper airway pressure resistance and hypopnea;

FIG. 6 shows a waveform of airflow from a sleeping patient which isindicative of a repetitive obstructive apnea;

FIG. 7 shows a waveform of airflow from a patient which is indicative ofa period of troubled wakefulness; and

FIG. 8 shows a waveform of airflow from a patient which is indicative ofa period of REM sleep with irregular breathing due to phasic REM in apatient.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of a system 1 according to thepresent invention. The system 1 may include a mask 20 which is connectedvia a tube 21 to receive airflow having a particular pressure from aflow generator 22. The amount of pressure provided to a particularpatient varies depending on patient's particular condition. Such amountof pressure may be determined utilizing any conventional PAP therapymethods.

The mask 20 covers the patient's nose and/or mouth. Conventional flowsensors 23 are coupled to the tube 21. The sensors 23 detect the rate ofairflow to/from patent and/or a pressure supplied to the patent by thegenerator 22. The sensors 23 may be internal or external to thegenerator 22. Signals corresponding to the airflow and/or the pressureare provided to a processing arrangement 24 for processing. Theprocessing arrangement 24 outputs a signal to a conventional flowcontrol device 25 to control a pressure applied to the flow tube 21 bythe flow generator 22. Those skilled in the art will understand that,for certain types of flow generators which may by employed as the flowgenerator 22, the processing arrangement 24 may directly control theflow generator 22, instead of controlling airflow therefrom bymanipulating the separate flow control device 25.

The system 1 may also include a continuous leak port or other ventingarrangement 28. The venting arrangement 28 allows for gases contained inthe exhaled airflow of the patient to be diverted from the incomingairflow to prevent re-breathing of the exhaled gases.

FIG. 2 shows an exemplary embodiment of a method according to thepresent invention. In step 202, the patient initiates the system 1 byplacing the mask 20 over his face and powering up the generator 22, theflow control device 25 and the processing arrangement 24.

In step 204, the system 1 initiates a real-time monitoring procedure ofthe patient's breathing patterns. The monitoring procedure is performedby the processing arrangement 24 which may utilize pre-stored patientdata along with current data provided by the sensors 23 regarding theairflow to and from the patient and/or the applied pressure.

During the monitoring procedure, the processing arrangement 24 makes adetermination as to a current state of the patient (e.g., whether thepatient is asleep, awake and breathing regularly or awake and breathingirregularly due to distress or anxiousness). Such determination can bemade based on a number of different measurements. For example, theprocessing arrangement 24 may analyze the patient's heart rate, bloodpressure EEG data, breathing patterns, etc. in the determining thepatient's state.

There are a number of characteristics of the patient's breathingpatterns that may be taken into account in making such a determination.FIGS. 3 and 4 show breathing patterns indicative of quiet, regular andrelaxed breathing in a patient during the PAP therapy. FIG. 3 isindicative of relaxed wakefulness (patient is not anxious ordistressed). FIG. 4 shows a period of relaxed breathing during sleepduring which the patient is correctly treated with the PAP therapy. Ineither case the applied pressure can be delivered without impairingcomfort. In addition, there are periods of sleep disordered breathingduring which the PAP therapy must be applied. Indices of sleepdisordered breathing include apnea (e.g., periods of zero airflow whichare greater than 8-10 seconds alternating with large breaths), hypopnea(e.g., cyclical periods of airflow which is substantially reduced,lasting 10 or more seconds, and terminated by larger breaths), orperiods of intermittent and cyclical change in the shape of the signal(e.g., characterized by flattening of the waveform, terminated by normalshaped breaths).

In contrast, the following exemplary characteristics may suggest thatthe patient is awake and anxious or distressed: pure mouth breathing(e.g., no signal from the sensors 23 which is configured to detect thepatient's airflow from the nose); erratic large breaths with varyinginspiratory times; irregularity of intervals between breaths (but notcyclic apneas which indicate sleep and the need for higher pressure,etc). FIG. 7 shows a period of such troubled wakefulness in which thebreathing pattern is characterized by irregularly variations in the sizeand/or frequency of breaths and/or irregular variation in the shapes ofthe patient's airflow tracing indicating that the patient is awake andeither anxious or uncomfortable. There is, however, no cyclical change(e.g., a periodic irregularity) in breath size, such as would be seenduring apnea and hypopnea sleep events. One of the ways to increase thepatient's comfort is to reduce the applied pressure when it is notneeded. Patients with obstructive sleep apnea do not require anypressure at all while awake. Thus, lowering the pressure applied to themask during such periods of irregular breathing should improve thepatient's comfort until the patient falls asleep (e.g., which may bemarked by the resumption of regularity or cyclical but regular periodsof obstruction easily recognized as apnea and hypopnea or elevated upperairway resistance).

The above-described breathing patterns are distinguishable from the slowmodulation in breath size and inspiratory timing seen, e.g., in CheyneStoke and other forms of obstructive apnea. FIG. 5 shows a breathingpattern of a patient on the PAP therapy which includes an event ofelevated upper airway resistance and hypopnea during sleep and FIG. 6show a breathing pattern corresponding to a repetitive obstructiveapnea. In both cases, the changes in breath size and frequency areslowly modulated and repetitive and cyclical (e.g., regularlyirregular). In these periods, the applied pressure is either needed ormust be raised, but there is no indication it is contributing to patientdistress. Thus, the applied pressure should not be lowered.

FIG. 8 shows a period of REM sleep. In this phase of sleep, whichoccurs, e.g., for 10-30 minutes every 90 minutes of normal sleep, abreathing pattern is often characterized by irregular breathing. Thispattern represents a potential exception to the use of irregularity toindicate wakefulness with anxiety. However, during this type ofbreathing, the patient is asleep and the applied pressure must bemaintained (i.e., not reduced as during wakefulness). The type ofirregularity seen during REM differs from that seen in wakefulness inseveral key parameters. This REM associated pattern of breathing mayinclude, e.g., the absence of larger breaths, especially after pauses,generally high respiratory rates and low flow rates, and a tendency forclustering of small breaths. These differences in the pattern of therespiratory airflow signal from those seen during troubled wakefulnessallow the separation of these states and can be used to make a change inthe applied pressure.

The processing arrangement 24 also collects and records data for eachpatient. Such data may be collected and entered manually by a technicianor automatically by the processing arrangement 24 itself. For example,the technician may monitor the patient's breathing and simultaneouslydetermine whether the patient is awake. Then, when the patient fallsasleep, the technician may mark the breathing patterns of this sleepingpatient so that the processing arrangement 24 may utilize this data infuture determinations as to whether or not the patient is awake. When adatabase of the patient's breathing characteristics has been built,determinations as to the patient's wakefulness may be made significantlymore accurate.

In step 206, the processing arrangement 24 determines whether there hasbeen a change in the patient's state. For example, the processingarrangement 24 may determine if the patient was asleep and has beenawakened; or the patient was awake and has fallen asleep. If there hasbeen no change, the processing arrangement 24 continues with themonitoring procedure.

If there has been a change in the patient's state, the processingarrangement 24 adjusts the pressure to correspond to the patient'scurrent state (step 208). For example, if the patient has been awakenedand the patient's breathing patterns indicate a period of troubledwakefulness as shown in FIG. 7, the processing arrangement 24 may reducethe applied pressure provided to the patient during such period. Thisreduction may be a complete elimination of the applied pressure (i.e.,the flow generator 22 reduces the flow rate to a level which does notprovide any net pressure to the patient in the mask, while maintainingonly the minimum sufficient flow through the circuit to the ventingarrangement 28 to prevent CO2 buildup), or a partial reduction (i.e.,the flow generator 22 produces only the flow sufficient to maintain areduced portion of the air pressure that it generates while the patientis asleep).

On the other hand, if the patient has fallen asleep, the processingarrangement 24 may instruct the flow control device 25 to elevate thepressure to the level to be applied while the patient is asleep. Forexample, this may be indicated where the patient's breathing patternschanged from the pattern shown in FIG. 7 to the pattern shown in FIG. 4.In such a case, the processing arrangement 24 should increase thepressure. From that time on, this increased pressure should not bereduced unless one of a plurality of predetermined breathing patterns isdetected. For example, the processing arrangement 24 should at leastmaintain the same pressure or, preferably, increase the pressure if thepatient's breathing pattern indicates an event of elevated upper airwayresistance and hypopnea as shown in FIG. 5. Also, the pressure should beat least maintained at the same value, or, preferably, increased, if thepatient's breathing pattern indicates a repetitive obstructive apnea asshown in FIG. 6, or if the patient shows irregular breathing whichsuggests he is in REM sleep, as during this type of breathing thepatient is asleep and the applied pressure must be maintained at thesame level as during other periods of sleep (i.e., not reduced as duringwakefulness).

In step 210, the processing arrangement 24 determines whetherinstructions to disengage the system 1 have been given. If suchinstructions have been given (e.g., if the patient has pressed adesignated button or a preset time limitation has expired), the system 1shuts down and ends all monitoring and flow generating activities.Otherwise, the system 1 continues with the monitoring procedure of step204.

One of the advantages of the system 1 according to the present inventionis that the pressure supplied to the patient is adjusted (e.g., reducedto zero or a preset low level) when the patient has an irregularbreathing pattern that suggests that he is awake and anxious. Whenbreathing is either regular (e.g., suggesting sleep) or shows sleepdisorder breathing events, the pressure may be maintained or increased.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the structure and themethodology of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover all modifications and variations of this invention whichcome within the scope of the appended claims and their equivalents.

1-28. (canceled)
 29. A positive airway pressure system for treatment ofa sleeping disorder in a patient, comprising: a generator supplyingairflow and applying a pressure to an airway of a patient; a sensormeasuring data corresponding to patient's breathing patterns; and aprocessing arrangement analyzing the breathing patterns to determinewhether the breathing patterns are indicative of one of the followingpatient's states: (i) a regular breathing state, (ii) a sleep disorderbreathing state, (iii) a REM sleep state and (iv) a troubled wakefulnessstate, the processing arrangement adjusting the applied pressure as afunction of the patient's state, wherein, when the breathing patternsindicate state (iv), the processing arrangement sets a target pressurevalue and controls the generator to adjust the pressure to approach thetarget pressure value.
 30. The system according to claim 29, wherein,when the breathing patterns indicate one of states (i) and (ii) and(iii), the processing arrangement transfers control of the generator toa therapeutic pressure adjustment arrangement.
 31. The system accordingto claim 29, wherein, when the target pressure value is reached, theprocessor holds the pressure at the target pressure value until thebreathing patterns change from a current state to one of states (i) and(ii) and (iii).
 32. The system according to claim 29, wherein theprocessor adjusts the pressure in predetermined increments to approachthe target pressure value.
 33. The system according to claim 30, whereinthe therapeutic pressure adjustment arrangement controls the generatoruntil the breathing patterns indicate state (iv).
 34. The systemaccording to claim 30, wherein the therapeutic pressure adjustmentarrangement executes a self-titrating algorithm to control the pressure.35. The system according to claim 29, wherein when the breathingpatterns indicate a change from one of states (i), (ii), (iii) to thestate (iv), the processing arrangement controls the generator to reducethe pressure.
 36. The system according to claim 30, wherein when thebreathing patterns indicate a change from state (iv) to one of states(i), (ii) and (iii), the processing arrangement transfers control of thegenerator to the therapeutic pressure adjustment arrangement whichincreases the pressure supplied by the generator.
 37. A method fortreatment of sleeping disorder in a patient using a positive airwaypressure, comprising the steps of: supplying an airflow to an airway ofa patient using a flow generator; measuring data corresponding to thepatient's breathing patterns; analyzing with the processing arrangementthe data corresponding to the breathing patterns to determine whetherthe breathing patterns are indicative of at least one of the followingpatient states: (i) a regular breathing state, (ii) a sleep disorderbreathing state, (iii) a REM sleep state, and (iv) a troubledwakefulness state; using the processing arrangement, controlling thegenerator to adjust the supplied pressure as a function of the patient'sstate; and when the breathing patterns indicate state (iv), controllingthe generator to adjust the supplied pressure to approach a targetpressure value.
 38. The method according to claim 37, furthercomprising: when the breathing patterns indicate one of states (i) and(ii) and (iii), transferring control of the generator, by the processingarrangement, to a therapeutic pressure adjustment arrangement.
 39. Themethod according to claim 37, further comprising: when the targetpressure value is reached, maintaining pressure at the target pressurevalue by the processing arrangement until the breathing patterns changefrom a current state to one of states (i) and (ii) and (iii).
 40. Themethod according to claim 37, further comprising: adjusting the pressurein predetermined increments to approach the target pressure value. 41.The method according to claim 38, further comprising: controlling thegenerator by the therapeutic pressure adjustment arrangement until thebreathing patterns indicate state (iv).
 42. The method according toclaim 41, wherein controlling step further includes the substep of:executing a self-titrating algorithm by the therapeutic pressureadjustment arrangement.
 43. The method according to claim 37, wherein,when the breathing patterns indicate a change from one of states (i),(ii), (iii) to the state (iv), reducing, by the processing arrangement,the pressure supplied by the generator.
 45. The method according toclaim 38, wherein, when the breathing patterns indicate a change fromstate (iv) to one of states (i), (ii) and (iii), increasing, by thetherapeutic pressure adjustment arrangement, the pressure supplied bythe generator.
 46. A system for monitoring breathing of a patient,comprising: a sensor measuring data corresponding to the patient'sbreathing patterns; and a processing arrangement determining whether thebreathing patterns are indicative of a troubled wakefulness state. 47.The system according to claim 46, further comprising: a patientinterface coupled to the sensor, the interface receiving an airflow ofthe patient.
 48. A method for monitoring breathing of a patient,comprising the steps of: measuring data corresponding to the patient'sbreathing patterns; and determining, based on the data, whether thebreathing patterns are indicative of a troubled wakefulness state. 49.The method according to claim 48, further comprising: determining, basedon the data, whether the breathing patterns are indicative of at leastone of the following patient states: (i) a regular breathing state, (ii)a sleep disorder breathing state and (iii) a REM sleep state.